Joe Herbert M.B, Ph.D.

Hormones and the Brain

Without Testosterone, Would There Be War?

War is a universal human attribute: does it depend on testosterone?

Posted Mar 06, 2016

Look at any video of the fighting in Syria.  You will see a collection of young men, crouching behind walls, firing their weapons (sometimes rather randomly), and, from time to time, they show dead adversaries, another row of young men.  Occasionally, during a lull, the men gather round their leader, another man, but noticeably older (but still not old).  The fighting in Syria is about power and possessions. It’s about who owns an area of land, because that land represents assets, both physical (crops, goods, resources etc) and psychosocial (political) control - who makes decisions, who rules.

This is why wars have been fought throughout history. There has never been a time, we can confidently say, when humans have not been at war somewhere in the world.  It's not a modern invention, and although the way it is carried out has changed dramatically over the ages, the reasons for war are more constant. One group of men (always men) want what another group of men has, or are defending themselves against another group who want what they have.  It may be land, water, food stocks, women; political control means access or control of these and other assets. Whatever the apparent ideology, the objectives of war have not altered. Anthropologists confirm the ancient heritage of war.  One study investigated 99 groups of hunter-gatherers from 37 different cultures, which are taken to represent a more primeval human condition.   68 percent were currently at war, 20 of the others had been at war within the last 5-25 years, and all reported having been at war at some time in the past.  The conclusion was that war is a universal property of human life.

War is not limited to humans. Baboons and chimpanzees live in stable and long-established groups.  If one group tries to take over the fruiting tree in the area if another, then there will be war.  But it’s a selective battle. It’s the males who invade the tree, and the males of the second group who defend their asset. Even though, within the group, males compete with one anther for status (and thus privileged access to food, shelter and females) in the face of a common threat they act collectively and cooperatively, even though the rewards for some may be minimal. Much has been made of the fact that chimpanzees rarely kill each other.  Is this a special propensity of humans?

Male chimps use their hands or their long canine teeth as weapons. These can be very effective: but to use them needs close contact and one chimp can easily run away from another. Chimps can throw rocks and sticks, but these are more gestures of defiance than aimed weapons.  It’s much harder to run away from a thrown spear, a flying arrow, a bullet fired from a rifle. Chimps have been known to catch and kill another.  Those who say that killing one another is a unique human trait confuse motivation with technology.

The male brain is exposed to testosterone from about 10 weeks after fertilization.  This results in permanent changes.  Little boys play in a more aggressive manner than girls, and this seem independent of culture though, of course, it can be moderated by parental influence.  As they pass through puberty, and are exposed to a second wave of testosterone, further aggressive traits appear (nearly all violent crime is committed by young men); together with the displays and risk-taking behavior that are familiar to us all. This has a purpose: it equips males for the competitive life they face – for mates, jobs, social dominance and so on.  Young males have a natural tendency, which seems testosterone-related, to form coalitions.  This includes collective violence and they seem curiously susceptible to a charismatic leader which sometimes leads to fanaticism.  It also equips them to defend their group.  Testosterone inclines males to like violence and use it as a strategy.  They also like taking risks; the majority of hang-gliders, off-piste skiers and road racers are young males.  Risk-taking is essential for successful competition: ‘nothing ventured, nothing gained’.  Without testosterone young men would be less eager to compete, defend their group, and attack other groups if there seems an opportunity for success and gain. It also equips men, particularly young men, for war.

But young men pay the penalty.  In the Second World War (1939-1945) about 75% of those killed in action were under 35 years of age.  Society encourages young males to prepare for war. Across many cultures, warriors and fighting prowess are prized.  In former times, military uniforms were brightly coloured and resplendent, recalling the sexual displays of males of some other species - for example: the intense colours on the face of mandrills or the bright blue scrotum of vervet monkeys.  Soldiers wore epaulettes to enhance their shoulder width, and helmets (eg bearskins) to emphasize their height, both masculine attributes.  Shakespeare wrote: ‘There is no love-broker in the world can more prevail in man’s commendation with women than report of valour’. So there’s a lot of sex in war.

How do we know all this depends on testosterone[1]?  Comparative and experimental studies show that interfering with the early actions of testosterone on the brain, or castration in adulthood, reduces aggressive tendencies, as any owner of a ‘neutered’ dog or cat will know. It also reduces the intolerance that males show towards males from other groups.  There are rare cases in which, because of a genetic mutation, human XY (male) embryos cannot detect or respond to their own testosterone.  Such individuals are born looking like females, and show none of the male-type behavior or aggressive traits that characterize males.  Often they are not diagnosed until puberty, when they fail to menstruate.

Testosterone does not cause war. War is caused by greed, revenge, a desire for domination, and political and social calculations of possible risks and benefits.  Testosterone is an essential contributor to the emergence of the war-like male endowed with the inclination to go to war. The history of humans seems to show that testosterone-driven attributes in man have made war inevitable. But will this always be the case? War has costs as well as benefits, and it appears that, whilst society has accepted the loss of young men, when civilians and homes and other assets are destroyed this alters the balance.  Civilian casualties in the First World War (1914-1918) were around 10% of those killed: only 25 years later, in the Second, they were 50%. The devastation produced by modern weapons and the effects this has on the civilian population are only too obvious in Syria. The cost of war is rising much faster than any benefit; atomic weapons are the ultimate example.  More recently-developed parts of the human brain, not directly responsive to testosterone, but involved in planning, decision-making and risk-assessment can moderate the ancient tendency of testosterone to instigate war.  The same brain that was responsible for the technical advances in weaponry that has made the risks of war so great.  Would we have been better off without testosterone? Would there have been no wars? It’s not a question worth asking, because without testosterone, which is essential for reproduction, there would be no humans (or fish, reptiles, birds and other mammals).  War has determined the fate of villages, tribes, countries; it shapes our maps. Testosterone, through war, is the molecule that has made our history.  We have had to pay a heavy price for these actions of testosterone; but the price is not fixed and is negotiable.

[1] A much fuller account of the pervasive social and biological actions of testosterone, written for a general readership, can be found in: Joe Herbert, Testosterone: sex, power and the will to win.  Oxford University Press, 2015